The present invention relates to an optical switch, and more particularly to an optical switch for switching optical signals as they are.
As optical communication systems have come into regular practical use in recent years, systems for providing entirely new functions and services have come to be conceived. Devices needed for such systems include an optical switch for switching the connections of many optical transmission channels at high speed.
As optical switches for this purpose, waveguide type switches utilizing the electrooptical effects of ferroelectrics such as LiNbO.sub.3 or of semiconductor materials such as GaAs and InP are extensively studied. For the structures of such switches are proposed a directional coupler type, as described in an article by M. Papuchon et al. in Applied Physics Letters, Vol. 27, 1975, pp. 289-291, and a crossover waveguide-based type like what is described in an article by Chen S. Tsai et al. in the IEEE Journal of Quantum Electronics, Vol. QE-14, 1978, pp. 513-517.
However, these optical switches involve the problem that, even where a dielectric substance having a relatively large electrooptical coefficient, such as LiNbO.sub.3, is used, the refraction index variation provided by the electric field is small and a high voltage is required for switching. To reduce the required switching voltage, the coupling length has to be extended for the directional coupler type, or the crossover angle narrowed for the crossover waveguide type, so that the switching voltage reduction and the switch size reduction tend to be mutually contradictory requirements. Therefore, it has been difficult to obtain a compact low-voltage optical switch of either type and to structure a multi-channel switch matrix by integrating many optical switches on a single substrate.